1. Technical Field
The present disclosure relates to apparatuses, systems and methods for providing energy to biological tissue and, more particularly, apparatuses, systems and methods for precise placement of microwave energy delivery devices during a surgical procedure.
2. Background of Related Art
Energy-based tissue treatment is well known in the art. Various types of energy (e.g., electrical, ultrasonic, microwave, cryogenic, thermal, laser, etc.) may be applied to tissue to achieve a desired result. Electrosurgery involves application of high radio-frequency electrical current to a surgical site to cut, ablate, coagulate or seal tissue. In monopolar electrosurgery, a source or active electrode delivers radio-frequency energy from the electrosurgical generator at a predetermined frequency to the tissue and a return electrode carries the current back to the generator. In monopolar electrosurgery, the source electrode is typically part of the surgical instrument held by the surgeon and applied to the tissue to be treated and a patient return electrode is placed remotely from the active electrode to carry the current back to the generator. In bipolar electrosurgery, the active and return electrodes are placed in close proximity to each other, e.g., at the surgical site, and electrosurgical currents are passed therebetween. In microwave electrosurgery, the antenna of the microwave energy delivery device generates electromagnetic fields in the adjacent tissue without the generation of electrosurgical currents between an active electrode and a return electrode as discussed hereinabove.
Radio-frequency energy may be delivered to targeted tissue in an ablation procedure by electrosurgical probes or by an electrosurgical antenna. In the case of tissue ablation using electrosurgical probes, electrode pairs are positioned in the surgical site to delivery high frequency electrosurgical currents between the pairs of active (+) and return (−) electrodes. An active (+) electrode and a return (−) electrode may be positioned in a spaced apart relationship on the shaft of an electrosurgical probe such that electrosurgical currents are passed along, or parallel to the shaft.
Alternatively, a first probe may function as an active (+) electrode and a second probe may function as a return (−) electrode. The first and second probes are positioned in a spaced apart relationship relative to each other such that electrosurgical currents are passed between the active (+) and return (−) electrodes resulting in the ablation of tissue positioned between the two probes. As such, the ablation region is defined by the spacing between the active (+) and return (−) electrodes and heating of tissue is typically confined therebetween. During ablation, current pathways in tissue between the active (+) and return (−) electrode produce localized heating between the two probes.
Radio-frequency energy in a microwave frequency range may be delivered to a targeted tissue by a microwave energy delivery device with a microwave antenna on the distal tip. The antenna of the microwave energy delivery device, when provided with a microwave energy signal, generates electromagnetic fields in the adjacent tissue without the generation of electrosurgical currents between an active electrode and a return electrode as discussed hereinabove.
While the ablation region produced by ablation probes is defined by the current path between the electrodes, the ablation region (shape and volume) produced by a microwave energy delivery device is defined by the type of antenna, the frequency of the microwave energy signal and the power level of the microwave energy signal. For example, an ablation region generated by a microwave energy delivery device may be symmetric about the tip and shaft of the microwave energy delivery device, directed to only one side of the shaft or if the antenna is unchoked, the ablation region may include a “tail” portion that extends proximally along the elongated shaft of the microwave energy delivery device.
Unlike radio-frequency probes, microwave energy delivery devices need not be configured to interact with each other. In fact, microwave energy delivery devices typically do not interact since any interaction would be due to the intermingling of the electromagnetic fields generated by the two devices (i.e., the two devices placed in close proximity may result in the overlapping of electromagnetic fields generated by each microwave energy delivery device). The overlapping electromagnetic fields may result in unpredictable results as the electromagnetic fields may cancel each other (resulting in no heating), the electromagnetic fields may combine (resulting in the generation of pockets of extremely high field densities) or any combination thereof. As such, controlling the spacing, and therefore controlling the interaction between microwave energy delivery devices becomes even more critical when the surgical procedures requires the insertion of a plurality of microwave energy delivery devices.
The unpredictable nature of the overlapping electromagnetic fields can be overcome by precisely placing the microwave energy delivery devices in a target tissue.